1. Field of the Invention
The present invention relates to a chucking device for removably holding a disk, a brushless motor provided with the chucking device and a disk drive apparatus equipped with the brushless motor. More particularly, the present invention pertains to a chucking device capable of accurately aligning the center of a central opening of a disk with the center of the chucking device.
2. Description of the Related Art
In recent years, the rotational speeds of a disk and a brushless motor for rotating the disk are increased as the operation of recording and reproducing the disk such as a CD, a DVD or the like becomes faster. At the present time, it is sometimes the case that the brushless motor is rotated at a speed of about 12,000 rpm. This brushless motor may suffer from vibration if a disk rotates with the center thereof misaligned with the center of the motor. As a chucking device that copes with the high speed rotation of the disk, there has been employed a structure that includes a cone having an annular slanting surface arranged to make contact with the entire extension of an inner circumferential surface of a central opening of the disk. The cone is movable along the axis of a shaft serving as a rotating shaft. Furthermore, the cone is axially upwardly biased by a resilient member such as a coil spring or the like (see, e.g., Japanese Patent Application Publication No. 2004-234773 for the structure of such a conventional chucking device).
As a disk drive apparatus becomes cheaper, there is an increasing demand for price reduction of the brushless motor with which the disk drive apparatus is equipped.
However, the conventional chucking device with the cone requires the use of an additional clamp member that presses the upper surface of the disk to keep the same in place. In addition, a resilient member such as a coil spring or the like is required in the conventional chucking device, which increases the number of parts of the chucking device. As a result, it becomes difficult to reduce the price of the chucking device, which in turn makes it difficult to achieve price reduction of the brushless motor provided with the chucking device.
Meanwhile, Japanese Patent Application Publication No. 2009-59410 discloses a chucking device including a cone, an annular yoke made of a magnetic material and a substantially annular clamp magnet. An annular recess is defined on the upper surface of the yoke. The yoke is arranged axially above the cone and fixed to a shaft. The clamp magnet is fixed to the upper surface of the yoke by an adhesive agent.
The adhesive agent is applied on a radially inward region of the recess when attaching the clamp magnet to the yoke. Thus, the adhesive agent is received within the recess as it spreads radially outwards. This prevents the adhesive agent from being pushed out of the yoke.
In the course of attaching the clamp magnet to the yoke, the clamp magnet is strongly pressed against the yoke by a magnetic attraction force acting between the clamp magnet and the yoke. When the adhesive agent is not uniformly applied on the upper surface of the yoke, there is a fear that the adhesive agent may be oozed out from between the yoke and the clamp magnet. When first fixing the yoke to the shaft and then bonding the clamp magnet to the yoke, the adhesive agent thus oozed may adhere to between the yoke and the cone and between the clamp magnet and the cone. This impedes movement of the cone. When first bonding the clamp magnet to the yoke and then fixing the yoke to the shaft, it would be possible to wipe out the oozed adhesive agent. However, the task of wiping out the adhesive agent is not easy to perform.